1. Field of the Invention
The present invention relates to an electronic device.
2. Description of Related Art
Portable terminal devices have been known in the art. For example, JP 2001-177889A discloses a wearable music player that comprises a band member for fitting the device body on a user body, and is capable of playing music based on music data while being fitted on the body.
In recent years, there have been known portable terminal devices for sports that measure and display biological information such as heart rate and pulse rate and exercise information such as exercise time, distance and pace when playing a sport or the like.
Such portable terminal devices are equipped with a secondary battery such as lithium-ion battery as a means for supplying an electric power necessary for operating components of the devices.
Secondary batteries such as lithium-ion batteries are rechargeable and also have high capacity with a comparatively small size. Accordingly, they enable small terminal devices, which have a limited room, to secure an electric power necessary for executing different measurement processing and display processing.
However, secondary batteries such as lithium-ion batteries may produce gas when they are subjected to an external impact or pressure or are deformed, e.g. devices are dropped on a floor by mistake with a battery installed, or when they are exposed to a severe temperature change (e.g. they are left in a high-temperature environment for a long time).
The gas produced from a battery can be released, if there is a small gap.
In this regard, most conventional devices equipped with a lithium-ion battery or the like are configured such that, even if gas is produced from the lithium-ion battery or the like, it can be released from a narrow gap. For example, digital cameras and the like are designed such that the battery is exchangeable, and therefore include a battery cover that is opened and closed every time the battery is exchanged. Further, cell-phones and the like include a gas-permeable membrane for a speaker or a microphone.
Even in a device having high air-tightness and waterproofness, there is a room inside the device to which gas produced from the battery can be released as long as the size of the device itself is sufficiently large with respect to the size of the battery, which prevents the inner pressure from rising to such a high level to cause rupture of the device.
On the other hand, portable terminal devices for sports are supposed to be exposed to sweat, rain and the like, and therefore require high waterproofness. Moreover, the size of such devices are as small as that of wristwatches, and even a narrow gap is not permitted if they are designed to have a highly airtight structure in order to improve the waterproofness.
When gas is produced from the lithium-ion battery or the like, it increases the inner pressure of a case. In the worst case, the increased pressure may break a case body or a display panel, or may blow off the display panel or the like that covers an opening of the case, which may result in an accident such as injury of a user wearing the device or a person near the device.